1. Field of the Invention
The invention relates to the field of saws for cutting wafers from bulk material and is more particularly applicable to the field of slicing monocrystalline wafers from monocrystalline boules.
2. Prior Art
Wafers for use in the electronics industries are generally sliced from monocrystalline boules using wafer saws. The newly sliced wafers are lapped and mechanically polished to remove saw damage such as gouges and surface unevenness. The mechanically polished wafers are surface etched to remove any surface damage caused by or not removed by the lapping and polishing. After etching, the wafers are ready for the beginning of the electronic device fabrication process.
Wafer production would be simpler and more economical, if as-sawn wafers were flat enough and smooth enough that the lapping and mechanical polishing steps could be eliminated. In order to achieve this goal, improvements are needed in the present wafer sawing process to provide much smoother as-sawn wafers.
Prior art wafer saw systems are of two main types. The first type completely severs each wafer from the boule as it is sliced. The second type utilizes an ingot comprised of the boule and a binding compound which holds the individual sliced wafers on the ingot. After a saw of the second type has sliced a number of wafers, the already sliced wafers are removed from the ingot as a group.
With wafer saws of the first type, there are problems with collecting the wafers and avoiding damage thereto. However the just-sawn surface of the wafer cannot be damaged by the saw blade during the return stroke of the blade because the wafer is not present during the blade return stroke. Scoring of the just-sawn face of the boule during blade return has been avoided by slightly retracting the face of the boule from the plane of the saw blade in order to provide enough clearance to prevent the blade from striking the boule during its return stroke. Systems of this type are disclosed in U.S. Pat. Nos. 2,960,978 and 3,702,604.
Unfortunately, no such protective systems are available for saws of the second type. As a result, both the just-sawn face of the wafer and the just-sawn face of the ingot are scored by the blade during its return stroke.